Lithium secondary battery

ABSTRACT

A lithium secondary battery includes: a battery case, and an internal electrode body  1  contained in the battery case and including a positive electrode  2 , a negative electrode  3 , and a separator  4  made of porous polymer. The positive electrode and the negative electrode are wound and laminated through the separator so that the positive electrode and the negative electrode are not brought into direct contact with each other. The battery case is composed of pure aluminum or aluminum alloy in which one or more components selected from manganese, magnesium, silicon and copper is added in aluminum. The lithium secondary battery has high weight energy density, is superior in safety, and is used for, particularly, an electric vehicle.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

[0001] The present invention relates to a lithium secondary batterywhich is superior in safety, and has high weight energy density (energystored per unit weight, hereinafter called “energy density”), and whichis suitably used for, particularly, an electric vehicle.

[0002] In recent years, the lithium secondary battery is being rapidlyand widely used to realize a small power source for portable electronicequipment. In addition, effort of development is being also made torealize practical use of the lithium secondary battery as a motordriving battery for an electric vehicle which replaces agasoline-powered vehicle, and as a battery for storing electric power inthe night.

[0003] The structure of lithium secondary battery is roughly dividedinto a wound type shown in FIG. 2 and a laminated type shown in FIG. 3.An internal electrode body 1 of the wound type is constituted by windinga positive electrode 2 and a negative electrode 3 through a separator 4,in which the positive electrode 2 with a large area or the like can becontained in a tubular container. In the case of this wound type, sinceit is sufficient that there is at least one lead 5 from each electrode2, 3, and, even if it is desired to lower current collection resistanceof each electrode 2, 3, it is sufficient to increase the number ofleads, there is an advantage that the internal structure of battery doesnot become complicated to make easy assembly of the battery.

[0004] On the other hand, an internal electrode body 7 of the laminatedtype is constructed by alternately laminating positive electrodes 8 andnegative electrodes 9 in multiple layers through separators 10, in whicharea per one positive electrode 8 or the like is no large, but theelectrode area of the entire battery can be increased by laminating themin multiple layers. The internal electrode body 7 being produced can bedesigned into any desired shape including a rectangular parallelepiped,cylindrical or tubular shape depending on the shape of each electrode 8,9 and the number of laminations. However, since a lead 6 is necessaryfor each electrode 8, 9, there is a disadvantage that the internalstructure of battery becomes complicated, and it is inferior to thewound type in view of assembly workability of battery.

[0005] In both the wound and laminated type structures, the internalelectrode body is housed in a metal battery case so that each electrodeand lead do not contact each other. Conventionally, stainless steel ismost widely used for this battery case, and sometimes nickel, titaniumor the like may be used.

[0006] However, since stainless steel or nickel has higher specificgravity, there is a disadvantage that, when it is used for the batterycase, the battery itself becomes heavy, so that the energy density islow. On the other hand, while titanium has an advantage to have lowerspecific gravity than stainless steel or nickel, and to be excellent incorrosion resistance, it is expensive, and its use is limited to aspecific application such as space development, so that it is difficultto be used as a general purpose battery component. In addition, in thelithium secondary battery, the battery case itself is often used as acurrent path for the positive or negative, and such material has highelectric resistance, leading to a cause of power loss. In addition, suchmetal is not always said to have good workability as the battery case.

[0007] Under such circumstances, a lithium secondary battery for anelectric vehicle (EV) or hybrid electric vehicle (HEV) is required tohave a cell capacity of at least 50 Wh, to have light weight not toincrease weight of the vehicle itself, and to have high safety. To meetsuch requirements, stainless steel with high melting point and highstrength has been conventionally used by particularly taking safety intoconsideration. However, as described earlier, it is difficult to solvethe problem for reducing weight of the battery. In addition, EV and HEVrequire a high current in acceleration, and, when the battery case isused as the current path, magnitude of electric resistance of thebattery case cannot be ignored, and there remains a problem onworkability of battery case the size of which is increased. Also, whennickel or titanium is used, such problems are also difficult to besolved because of physical characteristics of these materials.

[0008] Then, to solve such problems, the inventors have studied thepossibility to use aluminum as the battery case which has light weight,is excellent in electron conductivity, and of good workability. There isno precedent to use aluminum as a battery case for a large battery of 50Wh or more. This may be because the melting point of aluminum is asrelatively low as 660° C., a temperature significantly lower than thoseof the above materials, and, when the battery case is softened or melteddue to erroneous use or the like, electrolyte is feared to be evaporatedor burned, or exploded in the worst case.

[0009] According to Battery Association of Japan, as the “Guideline forSafety Evaluation on Secondary Lithium Cells” (commonly called “SBAGuideline”), it regulates that even if entire energy fully charged isinstantaneously discharged by external short-circuit or internalshort-circuiting caused by a nail piercing test or the like, and thenthe lithium secondary battery generates heat, the battery does not burstor fire.

[0010] While such safety is strictly required, the inventors found that,even when an aluminum battery case is used, the problems on safety couldbe solved by accurately measuring temperature rise on the surface of thebattery to calculate specific heat of the battery, and identifying therelationship between battery capacity and weight, and that reduction ofenergy density could be prevented by optimizing the battery case shape,and thus reached the present invention.

SUMMARY OF THE INVENTION

[0011] That is, according to the present invention, there is provided alithium secondary battery comprising:

[0012] a battery case, and

[0013] an internal electrode body contained in the battery case andincluding a positive electrode, a negative electrode, and a separatormade of porous polymer, the positive electrode and the negativeelectrode being wound or laminated through the separator so that thepositive electrode and the negative electrode are not brought intodirect contact with each other;

[0014] wherein the battery case is composed of pure aluminum or aluminumalloy in which one or more components selected from manganese,magnesium, silicon and copper is added in aluminum.

[0015] In addition, in the lithium secondary battery of the presentinvention, it is preferable in view of assuring safety of the batterythat a relationship of C(w·c)≦0.03 is established where current capacityis C (Ah), battery weight is w (kg), and specific heat of the battery isc (W/kg·° C.). It is also preferable in view of attaining both highenergy density and safety that a relationship of 0.004≦t/d≦0.04 isestablished where the battery case is cylindrical, its outer diameter isd (mmφ), and its wall thickness is t (mm). Moreover, such conditions arepreferably applied to a lithium secondary battery with battery capacityof 50 Wh or more. The lithium secondary battery satisfying suchconditions is suitably used as a battery for an electric vehicle or ahybrid electric vehicle. With this regard, the lithium secondary batteryof the present invention preferably uses lithium-manganese oxide(LiMn₂O₄) as positive active material.

[0016] As described above, the lithium secondary battery of the presentinvention reduces weight of the battery case while assuring high safety,so that it has a high energy density.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a sectional view showing a structure at the end of alithium secondary battery produced according to an embodiment.

[0018]FIG. 2 is a perspective view showing a structure of a wound-typeinternal electrode body.

[0019]FIG. 3 is a perspective view showing a structure of alaminated-type internal electrode body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] Now, embodiments of the present invention will be described, butthe present invention is not limited to these embodiments.

[0021] In the lithium secondary battery of the present invention, aninternal electrode body is composed by winding or laminating positiveand negative electrodes through separator films of porous polymer suchthat the positive electrodes do not directly contact the negativeelectrodes. Specifically, it includes structures shown in FIGS. 2 and 3,that is, internal electrode bodies 1 and 7.

[0022] The positive electrode used is an aluminum foil applied withmixture of positive active material and carbon powder to improveconductivity. As the positive active material, there can be used, forexample, lithium-cobalt oxide (LiCoO₂), lithium-nickel oxide (LiNiO₂),or lithium-manganese oxide (LiMn₂O₄). The present invention preferablyuses LiMn₂O₄. In addition, as the carbon powder, there can be used, forexample, acetylene black, graphite powder or the like. It is preferableto use high a purity material for the aluminum foil constituting thepositive electrode to prevent the battery performance from lowering dueto corrosion by an electrochemical reaction of the battery.

[0023] On the other hand, for the negative electrode it is preferable touse a copper foil coated with an amorphous carbon material such as softcarbon or hard carbon, or carbon powder such as natural graphite asnegative active material. Here, similarly to the aluminum foil used forthe positive electrode, it is preferable to use a high purity materialfor the copper foil used as the negative electrode to withstand thecorrosion due to an electrochemical reaction.

[0024] When the above-mentioned carbon material is used for the negativeelectrode, it is known that a part of the lithium ions adsorbed to thecarbon material at the initial charging reaction of the battery becomesthe so-called dead lithium which is kept adsorbed to the carbon materialand does not contribute to the subsequent charging and dischargingreactions, so that the capacity of the battery is lowered. Thus, it ispreferable to select a material in which the amount of the dead lithiumis small as the carbon material for the negative active material.

[0025] As a material of the separator film, it is preferable to use athree-layer structural material in which a polyethylene film havinglithium ion permeability and including micropores is sandwiched betweenporous polypropylene films having lithium ion permeability. This servesalso as a safety mechanism in which when the temperature of the internalelectrode body is raised, the polyethylene film is softened at about130° C. so that the micropores are collapsed to suppress the movement oflithium ions, that is, the battery reaction. When the polyethylene filmis sandwiched between the polypropylene films having a softeningtemperature higher than the polyethylene film, it is possible to preventthe contact between the positive and negative electrodes even aftersoftening of polyethylene.

[0026] The internal electrode body produced using such material ishoused in the battery case. The present invention uses a battery casecomposed of pure aluminum or aluminum alloy in which one or morecomponents selected from manganese, magnesium, silicon and copper isadded in aluminum. Here, pure aluminum does not refer to aluminum with100% purity, but may contain impurities which are unavoidably mixedduring an ordinary refining or manufacturing process, and, morespecifically, the purity is preferably 99% or more. In addition, as forthe aluminum alloy, it does not mean that impurities unavoidably mixedduring an ordinary manufacturing process are not similarly excluded fromaluminum which is the main component. Specific examples of aluminumalloy include alloy No. 3203 (aluminum-manganese alloy) prescribed inJIS.

[0027] Here, the aluminum battery case means that a main portion of thebattery case, that is, a container into which the internal wound body isinserted for storage is made of aluminum, and a sealing member forsealing an opening of the battery case is not necessarily made ofaluminum. For example, when the internal electrode body is a cylindricalwound body shown in FIG. 2, it is sufficient that at least a cylindricalcontainer opened at both ends, or a bottomed cylindrical containeropened at only one end is made of aluminum. When the internal electrodebody is a rectangular parallelepiped laminated body shown in FIG. 3, aslong as at least a tubular container with a rectangular section or arectangular parallelepiped box-like container opened only at one side ismade of aluminum, it is preferably used for the present invention.

[0028] The reason why the opening or the like through which the internalelectrode body is inserted is excluded from the battery case lies inthat the sealing member for sealing the opening of the battery case issometimes preferably constituted by an insulating material such as heatresistance resin or ceramics for the purpose of installing an externalterminal for taking out electric energy from the internal electrode bodyor isolating an electric path of the positive and negative electrodeswithin the battery. Of course, the above example of battery case doesnot exclude a battery case which can be entirely composed of aluminumfor the outer shell of battery by disposing insulating materials atappropriate locations to assure electric paths for the positive andnegative electrodes, and using an aluminum part for the sealing member.

[0029] Then, the battery is produced by the internal electrode body, thebattery case and other necessary members such as electrode terminals. Inthis case, as for the structure for the battery being produced, it maybe possible to adopt a structure which is a structure of a known smallbattery enlarged as it is. In addition, the inventors have proposed inJapanese Patent Application No. 9-202963 a structure of lithiumsecondary battery in which various pressure releasing mechanisms aredisposed at appropriate locations, and such structure may be preferablyemployed. Moreover, the battery thus produced preferably has at leastone pressure release valve which releases the battery internal pressureto the ambient air pressure when the battery internal pressure rises andreaches a predetermined pressure due to erroneous use of the battery orthe like, thereby preventing explosion due to rise of internal pressureof the battery.

[0030] According to the present invention, where current capacity of thebattery produced by using the aluminum battery case is C (Ah), thebattery weight is w (kg), and the specific heat of the battery is c(W/kg·° C.), the battery is preferably designed such that a relationshipof C/(w·c)≦0.03 is established. Here, the specific heat c of battery isdefined to be power (W) necessary for raising temperature of a batteryof 1 kg by 1° C. Therefore, even if the same battery case is used inproducing the battery, the battery has different specific heat ifcomponents other than the battery case differ, while, even if the volumeof battery is the same, the battery has different specific heatdepending on the material and wall thickness of the battery case, thesize of internal electrode body or the like.

[0031] However, when the construction conditions are established toassure safety even if all energy which the battery can store is used toraise temperature of the battery, that is, the battery is arranged suchthat the relationship of C/(w·c)≦0.03 is established, it is possible toobtain a battery in which temperature rise due to generated heat doesnot cause softening or melting of the battery case, and which can clearthe safety criteria of the SBA Guideline even if the energy charged inthe battery is instantaneously discharged as external short-circuitingis caused or as internal short-circuiting is caused by the nail piercingtest.

[0032] In addition, it is preferable in the present invention that therelationship of 0.004≦t/d≦0.04 is established where the battery case iscylindrical, the outer diameter of the battery case is d (mmφ), and thewall thickness is t (mm). For example, in the case where the batterycase has a thin wall thickness t when the outer diameter d of thebattery case is constant, that is, the value of t/d is small, the energydensity of the battery increases since the weight of battery case isreduced as the battery capacity is increased, and there arises a problemin safety since the strength of battery case is lowered. On the otherhand, in the case where the battery case has a thick wall thickness t,that is the value of t/d is large, it is desirable from the viewpoint ofsafety since the strength of battery case is heightened, but therearises a problem that the energy density is reduced as a whole since theweight of battery case is increased, and the battery capacity is alsoreduced,

[0033] Thus, when the battery is arranged to have a ratio of the outerdimension of battery case to the wall thickness in a specific range, itbecomes possible to assure safety while maintaining the energy densityof battery at a proper high value.

[0034] In the case where the battery case is a rectangularparallelepiped, the above relationship can be analogously applied byassuming that the outer diameter of a circle having the same area as thesection perpendicular in the longitudinal direction is the outerdiameter d of the battery case.

[0035] As described earlier, the present invention is attained as theresult of study mainly on the possibility of use of an aluminum batterycase for a battery with large capacity which has not been produced, andthe technical features of the present invention are suitably employed ina lithium secondary battery having battery capacity of 50 Wh or more.However, it is needless to say that there is no problem to employ thestructure of battery with large capacity for which the safety criteriaare strict as above for a battery with smaller capacity.

[0036] Thus, the battery with large capacity per unit cell produced byusing a battery case composed of aluminum has excellent advantages thatthe battery has lighter weight, and that it has higher energy density.When compared with a case where a plurality of batteries with smallcapacity are connected to obtain a battery with equivalent capacity,contact resistance due to battery connection can be reduced as thenumber of series/parallel connections is reduced in the battery, andmounting space for the battery can be saved. Therefore, the lithiumsecondary battery of the present invention is suitable in applicationssuch as the power supply for an electric or hybrid electric vehicle oras power supply for various mobile equipment.

[0037] Now, examples of lithium secondary battery according to thepresent invention are described, but it is needless to say that thepresent invention is not limited to these examples.

[0038] First, description is given of members commonly used for theexamples and the battery structure. The positive electrode was formed ofan aluminum foil coated with a mixture in which carbon powder (acetyleneblack) for improving the conductivity was added to lithium-manganeseoxide (LiMn₂O₄) as a positive active material. The negative electrodewas formed of a copper foil coated with graphite powder. As a separatorfor separating the positive electrode from the negative electrode, amicroporous separator made of polypropylene was used. The electrolytewas prepared by dissolving an LiPF₆ electrolyte in a mixed solution ofethylene carbonate (EC) and diethyl carbonate (DEC). The battery was acylindrical type which was formed by inserting a cylindrical internalelectrode body, in which the positive and negative electrodes were woundthrough the separator, into a cylindrical battery case, both ends of thecase being sealed with a structure shown in FIG. 1.

[0039] Here, in FIG. 1, a lead 32 for electricity collection connectedto either one of the positive or negative electrode (not shown) wasconnected to a metal rivet 33 as an internal terminal mounted on a disk34 for sealing a battery case 39. Then, the disk 34 was provided with apressure release valve 35 which was burst when the internal pressure ofthe battery reached a predetermined pressure, and crimped onto thebattery case 39 through ethylene propylene rubber 38 so that an externalterminal 37 was electrically connected to the disk 34 through a metalring 36, and that the disk 34, the metal ring 36 and the externalterminal 37 were electrically insulated from the battery case. Thus,there was formed a battery of cylindrical type with both terminals inwhich the external terminal for either one of the positive or negativeelectrode was disposed on one end of the battery case 39.

[0040] (Test for Selecting Battery Case Material)

[0041] Then, batteries in the battery size of outer diameter 50 mmφ andlength 245 mm and having the above-mentioned structure were formed byusing battery cases with outer diameter 50 mm and wall thickness 1 mmcomposed of various materials listed in Table 1, and energy density ofeach battery was measured. Here, aluminum alloy was aluminum added withmanganese, while SUS-304 was used as stainless steel. In addition, thedisk 34 for sealing the end of battery case 39 was made of the samematerial as the battery case 39, and area of the electrode was madeequal so that capacity of all batteries became 100 Wh. TABLE 1 Energydensity Battery case material (Wh/kg) Example 1 Aluminum 116 Example 2Aluminum alloy 115 Comparative example 1 Stainless steel  94 Comparativeexample 2 Nickel  89 Comparative example 3 Titanium 107

[0042] The energy densities of the produced batteries are also listed inTable 1. It is significant that a battery case material with higherdensity tends to provide lower resultant energy density. That is, in thecase of comparative example 2 where nickel with the highest density wasused as the battery case material, the energy density was the lowest of89 Wh/kg, and the energy density became higher as the density of batterycase material decreased in the order of stainless steel (comparativeexample 1), titanium (comparative example 3), and aluminum (examples 1and 2). Examples 1 and 2 using aluminum according to the presentinvention provided energy density of about 115 Wh/kg. Since the energydensity was 94 Wh/kg for comparative example 1 using stainless steelwhich had been generally used as the battery case material, thecharacteristic of energy density was improved by about 20% by usingaluminum or aluminum alloy for the battery case. Examples 1 and 2 werebelieved to have similar energy density because there was no significantdifference in density between aluminum and aluminum alloy. In addition,in this test, since the battery case was not used as a current path, anddistance was very short between the lead connected to the disk forsealing the battery case and the external terminal, impact on the energydensity due to difference of conductivity of the battery case materials(disk for sealing the battery case) used can be ignored.

[0043] (Test for Identifying Battery Case Shape)

[0044] Effectiveness in using aluminum for the battery case wasdemonstrated from the result of test for selecting battery case materialdescribed above. Then, batteries were produced with various wallthickness t by using aluminum for the battery case, fixing the outerdiameter d of the battery case to 50 mm, and length of the battery to245 mm, and varying the wall thickness t (mm) in view of improvement ofenergy density and securing of safety, and measured for energy densityand bulging (deformation) of the battery case after completing 100charging/discharging cycles with discharging rate of 0.2C and depth ofdischarge (D.O.D.) 100%. Table 2 lists values of t/d and results of theproduced battery cases. TABLE 2 Energy density Bulging after 100 t/d(Wh/kg) cycles (mm) Comparative example 4 0.002 141 >0.5 Example 3 0.004137 0.2 Example 4 0.01 130 0.1 Example 5 0.02 117 <0.1 Example 6 0.04101 0.0 Comparative example 5 0.06  82 0.0 Comparative example 6 0.1  570.0

[0045] Although the outer diameter of battery case is fixed, since theinner diameter of battery case is reduced as the wall thickness ofbattery case is thickened, the size of internal electrode body which canbe housed in the battery case is reduced, that is, the area ofelectrodes is made small, so that the absolute value of battery capacityis decreased. In addition, as the wall thickness of battery case isthickened, ratio of the battery case to the weight of entire battery isincreased. This increases the value of t/d as listed in Table 2. Thatis, as the wall thickness of battery case is thickened, the energydensity significantly tends to decrease.

[0046] Here, since comparative example 4 has as small t/d as 0.002, ithad a light battery case, and very high energy density of about 140Wh/kg. However, it has large bulging of outer diameter of battery caseafter the charging/discharging test of 100 cycles, and is found to havea problem in safety. On the other hand, comparative example 5 had aslarge t/d as 0.06, so that no deformation of battery case was observedafter the charging/discharging test of 100 cycles, but it could notprovide desired energy density of 100 Wh/kg or more due to increase ofweight of the battery case and decrease of volume of the internalelectrode body which could be housed in the battery case.

[0047] It is revealed from Table 2 that 0.004≦t/d≦0.04 is preferable asthe condition for assuring safety as well as output density of 100Wh/kg, as shown in examples 3 through 6. In addition, the mostpreferable characteristic can be attained with bulging suppressed to aslow as 0.1 mm or less while maintaining high energy density by making0.01≦t/d≦0.02.

[0048] (Test for Measuring Specific Heat of Battery)

[0049] Then, specific heat was measured on example 5 which had the valueof t/d of 0.02 or the wall thickness of 1 mm, which was believed to bepreferable from the viewpoint of the energy density and safety in theabove-mentioned test for identifying shape of battery case. The specificheat was measured by attaching a T-type thermocouple at the longitudinalcenter of side of battery, discharging the battery at a current of 27 Ato 2.5 V in a 25° C. constant temperature bath after constant currentcharging at 10 A and constant voltage charging at 4.1 V (6 hours intotal), and measuring temperature rise of the battery. As a result,temperature rise was 6° C. Assuming that all heat generation from thebattery when it is discharged is caused by internal resistance of thebattery, since the internal resistance of battery was 4 mΩ, total powerconsumption in discharge (resistance×(current)²×discharging time) was8923 W. Therefore, for battery weight of 0.86 kg and temperature rise of6° C., the specific heat of battery was calculated as 1729 W/kg·° C.

[0050] When all energy (100 Wh) of this battery was assumed to beinstantaneously discharged from the full charged state due to externalshort-circuiting caused by erroneous use or internal short-circuiting,since 100 Wh corresponded to 360000 W (100×3600 seconds), when thisvalue is divided by the weight and specific heat of the battery, thetemperature rise of the battery was calculated as 242° C., and it wasfound that the highest temperature reached was lower than the meltingpoint of 660° C. of aluminum. Then, when the external short-circuitingtest was conducted in a state where the battery was actually fullycharged, the pressure release valve was actuated but there was caused noburst or firing, so that safety of the battery was confirmed to beassured.

[0051] [Internal and External Short-circuiting Tests]

[0052] Batteries having various C/(w·c) values as shown in Table 3 wereproduced using an aluminum battery case by noticing the parameter ofC/(w·c) consisting of the battery capacity C (Ah), the battery weight w(kg), and the specific heat c of battery (W/kg·° C.) calculated with theabove method based on the result of the test for measuring specific heatof battery, and subjected to the nail piercing test (internalshort-circuiting test) according to the SBA Guideline. Table 3 alsolists the test results. TABLE 3 C/(w · c) Situation after testEvaluation Example 7 0.015 Pressure release valve actuated; ◯ good noburst nor firing Example 8 0.018 Pressure release valve actuated; ◯ goodno burst nor firing Example 9 0.03 Pressure release valve actuated; ◯good no burst nor firing Comparative 0.035 Pressure release valveactuated; X no good example 7 burst and firing occurred

[0053] As listed in Table 3, in the case of examples 7-9 with C/(w·c)value of 0.03 or less, although the pressure release valve wasactivated, no significant change of shape was observed due to softeningor melting of the battery case. However, in the case of comparativeexample 7 with C/(w·c) value of 0.035, the battery case wassignificantly deformed and partially cracked, and traces which werebelieved to indicate partial melting were observed. In addition, as forexamples 7-9 and comparative example 7, when similar batteries wereagain produced, and subjected to the external short-circuiting test byshort-circuiting the external terminal, there were provided the sameresults as the internal short-circuiting test shown in Table 3. Fromthis, it was confirmed that the safety criteria prescribed in the SBAGuideline could be passed by making the C/(w·c) value 0.03 or less.

[0054] As described, according to the lithium secondary battery of thepresent invention, since it uses for the battery case aluminum which haslightweight and is excellent in conductivity, it has a very excellentadvantage that the battery has light weight, and is significantlyimproved for the energy density than the prior art. Moreover, it ispossible to provide a battery with excellent safety which can pass thecriteria of SBA Guideline because the specific heat design of batteryfor the battery capacity and determination of shape of battery case areproperly conducted.

What is claimed is:
 1. A lithium secondary battery comprising: a batterycase, and an internal electrode body contained in the battery case andincluding a positive electrode, a negative electrode, and a separatormade of porous polymer, the positive electrode and the negativeelectrode being wound or laminated through the separator so that thepositive electrode and the negative electrode are not brought intodirect contact with each other; wherein said battery case is composed ofpure aluminum or aluminum alloy in which one or more components selectedfrom manganese, magnesium, silicon and copper is added in aluminum.
 2. Alithium secondary battery according to claim 1 , wherein a relationshipof C/(w·c)≦0.03 is established where current capacity is C (Ah), batteryweight is w (kg), and specific heat of the battery is c (W/kg·° C.). 3.A lithium secondary battery according to claim 1 , wherein arelationship of 0.004≦t/d≦0.04 is established where said battery case iscylindrical, its outer diameter is d (mmφ), and its wall thickness is t(mm).
 4. A lithium secondary battery according to claim 1 , whereincurrent capacity is 50 Wh or more.
 5. A lithium secondary batteryaccording to claim 1 , wherein it is used for an electric vehicle or ahybrid electric vehicle.
 6. A lithium secondary battery according toclaim 1 , wherein lithium-manganese oxide (LiMn₂O₄) is used as positiveactive material.